Pollination is widely recognized as an essential ecosystem service and a vital process to sustain food security [1
]. However, the impact of biodiversity erosion drivers, namely habitat loss and degradation, climate change, or the intensification of agriculture in the past half-century, has triggered a decline in wild and managed bees and other pollinating insects in several regions of the world [3
]. Agriculture poses many threats to insect pollinators, including changes in land use, loss, fragmentation and degradation of habitat, introduction of exotic organisms, modern agricultural practices, and pesticide use [9
]. The extensive use of insecticides (that can cause mortality by direct intoxication), herbicides and fertilizers (that can affect pollinators indirectly by decreasing floral resource availability) have been identified as the major drivers in the decline of pollinators [3
] and other insects [11
Diverse agricultural management practices are thus expected to influence wild bee abundance and richness on farms [12
]. Organic farming, for instance, can improve bee abundance, richness and productivity [13
], as long as sufficient habitat exists to maintain source populations [16
]. However, the effect of management practices on insect pollination in perennial crops seems to be less consistent than in annual crops [18
]. This could be a result of perennial systems usually having available a range of permanent structural elements such as hedgerows that can potentially attract pollinators, even under intensive management leading to low floral biodiversity [19
Apple (Malus domestica
) is one of the most important fruit crops globally, both economically and production-wise [21
]. Apple, together with a majority of agricultural crops worldwide, is dependent on animal pollination [2
]. The predominant pollination vector for apples are insects, such as bees (Insecta, Hymenoptera) and hoverflies (Diptera, Syrphidae). Their activity in orchards is thus essential for apple production globally [1
]. In addition, insect pollinators have been shown to promote increased quality of apples [24
] and pest management [25
], which are indirect and more difficult benefits to measure, but extremely important for the agricultural market. Studies examining the effect of management practices on apple insect pollination are still scarce [19
] and they report contrasting results. Available studies reported no differences in insect pollination between organic and conventional apple fields [19
] or higher flower visitation rate and species richness in organic orchards in comparison to Integrated Pest Management (IPM) orchards [26
]. In addition, results from studies assessing pollinator communities in conventional vs. abandoned or reduced-risk management apple orchards found either no differences [20
] or higher richness and diversity in abandoned orchards [28
]. Further studies examining these processes in apple cultivars are needed in order to draw patterns that are more general.
Additionally, there is still limited information on the condition of pollinators and the related ecosystem services they provide in oceanic islands, although recent research has demonstrated that insect pollinators play a key role in agricultural production [29
]. Previous studies have shown that oceanic insular ecosystems usually support less complex pollination networks with lower numbers of pollinator species, and that these mostly comprised generalist species [30
]. Thus, pollination networks on oceanic islands are probably the most vulnerable to disturbances [31
], including threats from intensive agricultural practices. The profound changes islands have experienced over the last century are known to have impacted several components of island ecosystems [33
] and diversity [34
], but little is still known about the current status of island ecological networks, and in particular, of pollinating insects.
In this study, we assessed the impact of agricultural management on apple pollination on an oceanic island (Terceira, Azores, Portugal), by comparing conventional (with and without herbicide application) and organic apple orchards. Both organic farming practices which do not employ agrochemicals and intensive practices that maintain an herbaceous cover are expected to result in higher pollinator visitation rates, species diversity and pollination service provision than in intensive management orchards without herbaceous cover. Additionally, we evaluated the impact of the surrounding landscape composition on apple pollination. We expect that the prevalence of intensive agriculture may have deleterious impacts on pollinator diversity and activity.
This study showed support for the increasing evidence that hymenopteran bee species and hoverflies, in addition to widespread honeybees, represent important pollination vectors for apple, further calling attention to the need of preserving wild pollinators in agroecosystems. In addition, results from this work suggest that management has a limited effect on apple pollination on an oceanic island, showing no significant effect on pollinator visitation rates and ultimately overall pollination services. On the contrary, a negative effect of increasing surrounding agricultural area on pollinator visitation was observed. Although conventional orchards without herbicides seem to benefit insect abundance at the orchard scale, together with favouring native species, they also showed a very uneven species distribution, leading to lower species richness and diversity than conventional orchards with herbicide application. These findings indicate that the effect of management in apple pollination may depend largely on habitat composition at the landscape level. Nevertheless, further studies are needed to gain a better understanding of the effect of these drivers on insect pollination in apple and other agroecosystems.